I am slim. weight 45. height is 5.7''. Is there any problem in putting weight since my father is also lean.

I am an 25 yr old guy. my weight is only 45 kgs. my height is 5.7''. I will try to put up the weight by eating more. but i cant exceed more than 46. If i get fever or anything for one day i will lose 3 to 4 kgs and to regain the weight i have to work on another 1 month. Since my father and grand father is also lean will that make any impact on my health so that i cant put on more weight. If not so what are the ways to increase the weight. Advance thanks in this regards.